Laboratory services

Biological mass spectrometry centre


Isotope ratio mass spectrometry

The isotope-ratio mass spectrometry section is equipped with two Thermo-Finnigan Delta XP continuous flow isotope ratio mass spectrometers.

Isotope ratio mass spectrometry is used to examine very small differences between stable isotopes of carbon (13C/12C), hydrogen (2H/1H), nitrogen (15N/14N) and oxygen (18O/16O). The mass spectrometers are able to analyse simple gases (e.g. CO2, H2)

One of the mass spectrometers (Surgery Unit) is equipped with a GC / combustion/ high temperature conversion interface to allow the user to examine the stable isotope enrichment of e.g. carbon in fatty acids (by quantitative combustion of the peak eluting from the GC to CO2) or hydrogen in amino acids (by quantitative pyrolysis / high temperature conversion of the peak eluting from the GC to H2). This is ideally suited to tracer studies where the metabolic fate of a precursor can be followed (e.g. in vivo incorporation of an amino acid precursor into a protein). The GC is equipped with a split-splitless injector and with a PTV (programmable temperature vaporization) injector to allow large volume injection.

The other mass spectrometer (Nutrition Unit) is equipped with an automated gas equilibration / injection unit. This allows analysis of CO2 from breath samples (by direct injection) or analysis of 2H/1H or 18O/16O in water after equilibration with H2 or with CO2. This is used for three types of measurement:

  • Body composition and energy expenditure. If a subject is given an oral dose of 2H2O, then measurement of 2H2O in saliva or urine gives information on total body water, fat mass, fat-free mass and % body fat. If H218O is given simultaneously with 2H2O, then total energy expenditure can also be measured. More details about body composition and energy expenditure.
  • Breast milk intake. Another type of investigation using 2H2O is the measurement of breast milk intake. It is very difficult to accurately measure breast milk intake, but if an oral dose of 2H2O is given to the mother and urine samples are taken from the mother and the infant, then the amount of breast milk taken in by the infant can be accurately calculated. More details about breast milk intake.
  • 13CO2 breath tests. Measurement of 13CO2 in breath can yield useful information about different processes in the body. We are currently using these breath tests for measurement of: absorption of gas absorbed during laparoscopic surgery, gastric emptying time (13C-octanoic acid), liver mitochondrial metabolism (13C-methionine), comparison of utilisation of different starches. Other 13C-breath tests have been used for assessment of Helicobacter pylori infection (13C-urea), pancreatic function (13C-mixed triglyceride), bacterial overgrowth (13C-xylose) etc.

If you have any interest in using these machines or techniques, please contact Dr Simon Eaton or Dr Jonathan Wells in the first instance.

Page last modified on 07 jun 10 10:18